The failure mechanism of giant loess-mudstone landslides under complex three-dimensional groundwater conditions remains a critical challenge in geohazard assessment, particularly in the transition zone between the Qinghai-Tibet Plateau and the Loess Plateau. Taking the 2022 Hongya Village landslide (volume > 21 million m³) in Qinghai Province as a typical case, this study investigates its hydro-mechanical coupling mechanism and kinematic evolution through an integrated approach combining InSAR time-series analysis, field investigations, in-situ hydrological testing, and laboratory geotechnical tests.
The results reveal that the landslide was driven by a multi-source composite hydrogeological network rather than single surface rainfall infiltration. This complex system consisted of shallow vertical rainfall infiltration, continuous lateral recharge from an upstream landslide, and strong basal confined water with an artesian head of 17 to 24 m. This hydro-mechanical coupling induced super-pore water pressure and severe water-softening, leading to a sharp decrease in effective stress and significant degradation of the shear strength in the binary sliding zones. Kinematically, the landslide exhibited a progressive "toe-traction and head-pushing" failure mode. The intense shearing and subsequent static liquefaction of the extremely thick saturated basal loess triggered a rapid phase transformation from a solid block slide into a high-speed debris flow. Furthermore, the geometric combination of bedrock structure and sliding direction strictly controlled the zoned failure modes across the site.
These findings provide a vital quantitative basis for the early identification, dynamic risk assessment, and disaster mitigation of deep-seated composite landslides in fragile geological environments.
 

Loess-mudstone landslide; Hydro-mechanical coupling; Confined water; Static liquefaction; Kinematic evolution; InSAR